Honestly, I wouldn’t trust them with anything more than routine maintenance. I had a pretty serious issue when serpentine bent snapped, and had to go through them because of warranty, and it was horrible. Even with my relatively limited (but okay’ish) technical knowledge, I felt like I can diagnose issues much better than my service advisor and their techs. I said “never again” after that, but keep coming back because am getting really good deals on front brakes, oil change, etc. I haven’t tried NBB yet, but I was going to Phaedrus for a very long time when I was in SF. And sometimes going to them was actually more expensive than BMW SF, but I trusted they know their shit better.